JPS606636A - Recovery of useful component from exhaust gas - Google Patents

Abstract

PURPOSE:To absorb and recover the unreacted raw material from exhaust gas, by neutralizing and concentrating the waste sulfuric acid solution discharged from the methacrylic acid alkyl ester (MAE) production process under the condition to generate steam from the inside of the liquid layer, and contacting the obtained steam-based gas with water or an alkaline aqueous solution under a non-condensing condition. CONSTITUTION:Methacrylamide or methacylic acid is made to react with a lower aliphatic alcohol in the presence of sulfuric acid to produce MAE. The waste sulfuric acid solution is introduced into the ammonium sulfate saturation tank 10 and neutralized with ammonia, while introducing steam 01 into the bottom of the tank. The produced steam-based exhaust gas is introduced (20) into the vapor-liquid contacting column 30 and made to contact with water or an alkaline aqueous solution 60 under a condition capable of handling the exhaust gas as a non-condensing gas (the condition can be achieved by keeping the temperature of the system at >=98 deg.C). Methacrylamide and methacrylic acid can be recovered (100) by this process. The exhaust gas from the contacting column 30 is introduced into the preliminary condensation column 120 to effect the partial condensation (20-60%) in the presence of an inert gas, then into the total condensation column 150. The condensed liquid is sent to the alcohol distillation and recovery column with the pump 180.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating and recovering useful components such as methacrylamide from components discharged from a methacrylic acid alkyl ester (hereinafter also referred to as MAE) production process.

MAR is produced by esterifying methacrylamide (hereinafter also referred to as MAM) or methacrylic acid (hereinafter also referred to as MAA) with lower fatty acid alcohol (hereinafter also referred to as ROH) in the presence of sulfuric acid.

The lower fatty acid alcohols mentioned here include methanol,
Alcohols having about 1 to 6 carbon atoms, such as ethanol, isopropanol, normal propazol, isobutanol, normal butanol, pentanol, and hexanol.

The esterification reaction is carried out at a normal reaction temperature of 60°C to 150°C.
, reaction time (residence time in case of continuous reaction) 30 minutes ~ 2
The process is carried out for about 40 minutes under suitable conditions, and from the Nisderization reaction solution thus produced, the target product MAR, most of the unreacted raw materials, and a part of MAM are distilled, extracted, and removed.
It is separated by two predetermined operations such as stripping, and the separated residual liquid is discharged from the esterification process as a waste liquid (hereinafter referred to as waste sulfuric acid liquid) containing a high concentration of sulfuric acid and ammonium bisulfate.

A common method for treating such waste sulfuric acid solution is to neutralize the waste sulfuric acid solution with ammor in a treatment tank called an ammonium sulfate saturation tank to form ammonium sulfate (ammonium sulfate), and then heat and concentrate and crystallize it to recover it as by-product ammonium sulfate. It is something to do.

(Instead of neutralization with ammonia, it is of course possible to neutralize with other inexpensively available alkalis, such as caustic soda, caustic potash, milk of lime, etc.) In that case, mirabilite, gypsum, etc. are produced as by-products. ) However, the waste sulfuric acid solution usually contains several percent of unreacted raw materials such as MAM, MAA, and ☆OH, but these components are removed when the waste sulfuric acid solution is subjected to the neutralization heating concentration crystallization treatment. During the process, most of it denatures into tar-like components, which adhere to by-product ammonium sulfate crystals and are discharged. - However, by-product ammonium sulfate etc. mixed with such tar-like substances not only have low commercial value, but also
It is also undesirable from the viewpoint of improving the unit consumption of MAR, which is the target substance, that useful unreacted components such as AM and MAA are denatured into tar-like substances and lost without being recovered.

As a result of intensive studies in view of the above points, the present invention, etc. has conducted the above-mentioned neutralization heating concentration in such a way that water vapor is effectively generated from inside the waste sulfuric acid liquid layer, thereby producing water vapor that generates these unreacted useful substances. By performing an appropriate stripping operation (diffusion operation) in conjunction with this, it is possible to take it out of the system without turning it into tar, and by applying appropriate means, it is possible to recover it with a high yield. They discovered this and completed the present invention.

That is, the present invention:

(1) In a method for producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify the waste liquid containing the sulfuric acid discharged from the esterification step. (hereinafter referred to as waste sulfuric acid solution) is neutralized with alkali.
When concentrating and recovering sulfate, unreacted methacrylamide and/or methacrylamide in the waste sulfuric acid solution is neutralized and concentrated by effectively generating water vapor from inside the waste sulfuric acid solution layer. A gas absorption operation in which the acid is separated from the waste sulfuric acid solution by entraining it with the generated water vapor, and the water vapor-based exhaust gas is brought into contact with water and/or an aqueous alkali solution under conditions where it can be treated as a substantially non-condensable gas. A method for recovering active ingredients from exhaust gas (hereinafter referred to as invention 1), characterized in that the separated methacrylamide and/or methacrylic acid is absorbed and recovered in the water and/or alkaline aqueous solution.

(2) A method for producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify it, which contains the sulfuric acid discharged from the esterification step. The waste liquid (hereinafter referred to as waste sulfuric acid liquid) is neutralized with alkali.
When concentrating and recovering sulfate, unreacted methacrylamide and/or methacrylamide in the waste sulfuric acid solution is neutralized and concentrated by effectively generating water vapor from inside the waste sulfuric acid solution layer. The acid and lower aliphatic alcohol are entrained in the generated steam and separated from the waste sulfuric acid solution, and the steam and the exhaust gas are mixed with water and/or an aqueous alkaline solution under conditions that can be treated as a substantially non-condensable gas. The methacrylamide and/or methacrylic acid is absorbed into the water and/or alkaline aqueous solution and recovered by contacting and performing a gas absorption operation, and is recycled to the esterification process to be recovered as a methacrylic ester. It is obtained by first partially condensing 20 to 60% of the condensed components in the presence of an inert gas to remove them from the steam-based exhaust gas after the process has been carried out, and then completely condensing the remaining uncondensed portion. A method for recovering active ingredients from exhaust gas (hereinafter referred to as invention 2), characterized in that a condensate containing a lower aliphatic alcohol is recycled and reused in the ertherization step.

exists in

Hereinafter, the constituent elements of the present invention will be explained in detail while being separated.

First, invention 1 will be explained.

In the present invention, when the waste liquid containing sulfuric acid (waste sulfuric acid liquid) discharged from the esterification process during MAR production is neutralized and concentrated with an alkali and recovered as sulfate, the neutralization and concentration are This is done so that water vapor is effectively generated from inside the waste sulfuric acid liquid layer.

Various methods can be adopted for this purpose, but for example, ammonia gas for neutralization is introduced into the lower part of the ammonium sulfate saturation tank, and the neutralization reaction is mainly caused in this part, and the heat generated causes water vapor to be removed from the inside of the liquid layer. A large amount of water vapor may be generated, or a heating tube (heating coil) may be inserted into the layer and a stirrer may be provided to generate water vapor from the inside by stirring vigorously at the same time as heating.

As another method, the neutralization may be carried out while blowing steam into the waste sulfuric acid solution, and the heating and stirring may be performed mainly by the steam. Of course, some of these means can also be used in combination.

In addition, when adopting the steam blowing method, the flow rate of the steam blowing is not particularly limited, but is usually 50 to 500 rr per 10 rd/hr of waste sulfuric acid solution to be treated.
R/hr is appropriate. Also, the temperature at that time is 1
A temperature of about 00 to 125°C is adopted. The time for the blowing treatment (in the case of treatment by continuous reaction, it is the residence time of the waste sulfuric acid solution in the treatment tank) may vary depending on the flow rate of steam blown, the treatment temperature, etc., but it is usually 0.5 to 3.0 hours. is sufficient.

As a result, unreacted MAM and/or MAA in the waste liquid is removed from the system along with the generated water vapor and separated from the waste sulfuric acid liquid. That is, by applying a stripping operation using water vapor, MAM and the like in the waste sulfuric acid solution are quickly separated from the system without turning them into tar.

A further preferred embodiment is to simultaneously blow in an inert gas to the active ingredient to be recovered when steam is blown in as described above.

The inert gas mentioned here means a non-condensable gas that does not react with useful components such as MAM to be recovered. Such inert gases include nitrogen, oxygen, air, helium,
Examples include neon, argon, methane, carbon dioxide, etc., but air is preferable from the viewpoint of ease of handling.

The amount of the inert gas blown is not particularly specified, but it is usually set to a volume ratio of about 1 to 10% to the water vapor in the exhaust gas (mainly composed of water vapor and inert gas) after the dispersion operation. desirable. Under such operating conditions, components with a higher boiling point than water are also stripped in high yield and removed from the waste sulfuric acid solution into the gas phase.

The water vapor exhaust gas obtained in this way (usually 100 to 11
However, in a large amount of water vapor, the recovered active ingredient MAM etc. is discharged at 0℃ and normal pressure.
% (weight), so in order to use it effectively, it is necessary to avoid entraining water as much as possible from the gas with this composition.
M.

It is necessary to separate MAAS ROH.

In this case, the means usually adopted is to first condense the entire amount of the water vapor exhaust gas to obtain a dilute aqueous solution such as MAM,
This is distilled and concentrated again. However, it should be noted here that the target components to be recovered, MAM and MAA (and in some cases ROM as well), have a higher boiling point than water, so they remain in the can of the distillation column, and water is released from the top of the column. Most of it is distilled. In other words, if such an operation is adopted, a large amount of energy will be applied to recover a small amount of the active ingredient, and a large amount of water vapor will be cooled and condensed, which will then be heated and evaporated again, so from an energy saving standpoint, This would have to be an extremely irrational operation that is completely unacceptable.

However, in the present invention, as described above, a large amount of steam-based exhaust gas containing MAM etc. at an extremely low concentration of 0.5 to 2% (in some cases, an inert gas such as air as described above) is used. The gas absorption operation is carried out by bringing the gas into contact with water/alkaline aqueous solution under conditions where it can be treated as a substantially non-condensable gas.

What I would like to draw attention to here is that such gas absorption operations themselves are well-known operations in chemical engineering, but they all remove carbon dioxide, hydrogen sulfide, etc. from non-condensable gases such as air. It absorbs water by bringing it into contact with an aqueous solution such as ethanolamine, and the idea of carrying out an operation in which water vapor, which is a condensable gas, is brought into contact with an aqueous absorption liquid as in the present invention is unprecedented in the field of firewood. Good morning.

In the present invention, the conditions under which steam-based exhaust gas can be treated as a substantially non-condensable gas are the conditions in which the condensation of its condensable components, particularly water vapor, is kept within the range of 5% or less, preferably 2% or less. says. These conditions depend on the amount of inert gas mixed in with the water vapor, but are usually achieved by maintaining the gas-liquid contact system at a temperature of at least 98°C. For this purpose, for example, the water vapor gas to be treated must be
It is desirable to maintain the temperature at 5 to 115°C, preferably around 110°C, before introducing it into the system, and to supply the absorption liquid described below after heating it to 70°C or higher, preferably 80°C or higher.

In the present invention, physical absorption using water as the absorption liquid is sufficient to achieve the objective, but in order to achieve an even higher effect, it is recommended to carry out reactive absorption using an aqueous anolytic solution. is more desirable. As such alkali, any one such as caustic soda, caustic potash, soda carbonate, potash carbonate, etc. can be used.

In this case, it is preferable to control the pH of the absorption liquid obtained by absorbing MAM and/or MAA to be maintained in the range of 7 to 1O1, particularly around 8. If the pH is less than 7, MAM etc. will not be absorbed sufficiently, and if it exceeds 10, no further improvement in the absorption effect can be expected.
This is not desirable because the amount of the alkali salt (for example, in the case of caustic soda, Glauber's salt is mixed as a by-product) mixed into the by-product ammonium sulfate and the like increases, reducing its commercial value.

In addition, the amount of water or alkaline aqueous solution supplied from outside for absorption (naturally, this is approximately equal to the amount of water or alkaline aqueous solution extracted in a steady state)
It is desirable that the amount is as small as possible while still achieving the purpose of the present invention, and in particular, it is preferably kept within the range of 1% to 10% by weight of the condensable component (mostly water vapor) of the steam-based exhaust gas.

As described above, MAM, M
AA is recovered as an aqueous solution by contact absorption with burqa, water solution, etc., and since the operation is carried out under conditions where the water vapor system can be treated as a substantially non-condensable gas, the aqueous solution of MAM etc. obtained in this way is Since it is very concentrated, it is recycled to the esterification process and MAR again.
It can be recovered as.

The device for carrying out the gas-liquid contact operation of the present invention includes:
Any known device for performing gas-liquid mass transfer operation as a unit operation, such as a packed column, plate column, or spray base ring, can be employed. In addition, when a packed column is used, the packing material may be a rashich ring, a ball ring, a burl saddle ring, a McMahon ring, a telleret ring, a navel ring, or the like.

Furthermore, as mentioned above, in the present invention, it is desirable to use as small an amount of the absorption liquid as possible in order to maintain the water balance when reusing it in the esterification process. L/G) may become too small, making it difficult to ensure efficient gas-liquid contacting operations within the gas-liquid contacting device. In such cases, a large flow rate of absorption liquid should be circulated within the device to supply a sufficiently large amount of absorption liquid to the middle section of the tower to ensure good gas-liquid contact with the steam-based exhaust gas rising from below. At the same time, a part of the circulating absorption liquid is extracted from the bottom of the tower, while fresh (uncirculated) absorption liquid is supplied from the top of the tower, completely absorbing the active ingredients that could not be absorbed at the bottom of the tower. It is preferable to do so.

In addition, the method of contacting water and/or alkaline aqueous solution as an absorbing liquid with steam-based gas may be either countercurrent operation or cocurrent operation, and may be a liquid one-pass type (non-circulation type), liquid circulation type, or a combination thereof. can also be adopted. As mentioned above, the aqueous alkaline solution, etc. may be supplied at the top of the tower in the case of a one-pass system, but in the case of a circulation system, the uncirculated absorption liquid is supplied to the top of the tower, and the circulating liquid is supplied to the circulating liquid section in the middle stage. You can also do that. In this case, these fluctuations can be effectively dealt with by adjusting the flow rate ratio of uncirculated liquid and circulating liquid according to the composition ratio of MAM and MAA contained in the steam gas system.

Furthermore, it is also possible to use a plurality of contact towers having different absorption liquid compositions connected in series. The various factors mentioned above are balanced and absorbed depending on the composition ratio of MAM and MAA in the exhaust steam system to be treated. The most effective contact method can be determined by selecting and employing the optimal combination of operating conditions after considering the system.

As described above, in the present invention, the gas absorption operation is performed under conditions in which the water vapor exhaust gas can be treated as a substantially condensable gas, so that the MAM recovered by being absorbed by an aqueous alkaline solution, etc. , MAA, etc. can be obtained as a liquid with a sufficiently high concentration, so when it is reused, it can be used as it is without any pretreatment such as concentration. For example, as a reuse method, this absorption liquid can be recycled to the esterification process and recovered as MAR, but even in such a case, it is possible to carry out the process as it is without destroying the water balance of the esterification process. I can do it. This is because the esterification reaction is a reversible reaction, and when a large amount of water is introduced into the system, the generated MAR may decompose and return to MAA.

In addition, even if the aqueous alkali solution absorption liquid is circulated to the esterification process, the small amount of alkali is easily neutralized by the excess sulfuric acid present in the reaction system of the esterification process, so there is no effect on the esterification reaction itself. There will be no impact.

Although MAM and MAA are originally polymerizable components, it has been found that when handled under such alkaline conditions, no tendency for polymerization is observed.

Next, invention 2 will be explained.

Invention 2 is to recover not only MAM and/or MAA but also lower fatty acid alcohol (ROM).

Regarding the constituent elements of the first half of Invention 2, the same as described in Invention 1 applies. However, unlike MAM, etc., the ROH accompanying the steam-based exhaust gas generated by processing the waste sulfuric acid solution is not substantially recovered in the gas absorption operation using the alkaline absorption liquid in Invention 1, so it is discharged from the gas-liquid contact device. The steam-based exhaust gas still contains a considerable amount of the alcohol.

In the present invention, 20 to 60%, preferably 45 to 60% of the steam exhaust gas that has been subjected to the absorption treatment is first removed by condensing it in the presence of an inert gas as described above. .

It is necessary that the inert gas be present in an amount of 1 to 10% by volume relative to the condensable component, but when performing the partial condensation in this way, by making the above specified amount of inert gas exist, In the vapor-liquid equilibrium relationship of the ROH-water system, it appears that the equilibrium vapor pressure of the alcohol above is significantly increased, and most of the alcohol (more than 85%) goes directly to the next condensation operation without being condensed. and pass.

Conversely, since the alcohol concentration in the preliminarily condensed water vapor is extremely low, even if this condensed water is not collected and is eventually disposed of, the loss of alcohol will be minimal. Furthermore, since the COD value is low, the burden of wastewater treatment is extremely small.

The inert gas used here and the steam-based exhaust gas from which MAM and the like have been removed may be mixed in the pipe on the way from the gas-liquid contact tower to the pre-condensation tower, for example, or
Alternatively, they may be mixed in a precondensation tower. Moreover, as a more preferable and easy means, it is also possible to blow an inert gas together with the steam in the first step of blowing steam into the waste sulfuric acid solution and mix it at this stage.

As the device for carrying out the preliminary condensation operation, a multi-tube type, spiral type, or double-tube type condensing heat exchanger (condenser), which is commonly used for condensing steam, is suitably used.

As mentioned above, the alcohol concentration in the steam exhaust gas that passed through the pre-condensation tower without being condensed was approximately 1.94 times higher than that of the gas before treatment. Next, the condensed components in the steam-based exhaust gas are completely condensed (that is, total condensation) to obtain a condensate containing RO.

(Of course, the non-condensable inert gas is separated by the condensing group without being condensed.) The alcohol concentration in the condensate is extremely low due to the preliminary condensation operation as described above. However, even if the water is easily separated by entering the alcohol distillation recovery column G and concentrating it to at least 60% or more, preferably about 80% or more, the water is recycled as it is to the esterification process. Don't break the lance (you can effectively recover it).

As a device for carrying out the total condensation operation, a device similar to that used for preliminary condensation, ie, a multi-tube condenser, etc., is suitably used.

It should be noted that the condensation operation used in Invention 2 is a simple cooling operation (with almost no number of stages), and therefore is used for cooling without any thermoeconomically problematic distillation operation. It should be noted that such concentration recovery is effected only by the energy provided.

The embodiments of the present invention will be described below with reference to Examples, but these are merely illustrative, and the technical scope of the invention stipulated in Article 70 of the Patent Law should not be construed as being limited by these. No.

, Example-1 Figure 1 shows a flow sheet for the equipment used in the experiment.

10 is an ammonium sulfate saturation tank. The waste sulfuric acid solution is received in the saturation tank and neutralized with ammonia, and at 110°C, 80.0 g/llr of water vapor and 511 kg/l of air are passed from piping 01 through the tank blow-in pipe installed at the bottom of the saturation tank.
A stripping operation was performed by blowing in Hr. The generated water vapor exhaust gas is MAM 10.8 Kg/Hr,
MAA 14.0 Kg/Ilr.

M e OH40.0Kg/llr, water vapor 400
0.0Kg/Hr.

Air has a composition of 511.0 Kg/Hr, and is introduced into the gas-liquid contact tower 30 through the pipe 20 while being maintained at 110°C. Gas-liquid contact tower is 0.9mφ*
, 16.0 mL of empty column G, 2 inches of Rashihi rank, recovery IB 40: 6. Om, I-layer top 1s 50 near, 0m filled. Friends
Approximately 7% caustic soda aqueous solution is used as a nosh absorption liquid.
At a flow rate of 1.0 kg/11r, the distribution pipe 60 at the top of the column is supplied to the recovery section 40 at 80°C, and the circulating liquid 70 at the bottom of the column is supplied to the J-minf.

80 through pipe 90 at 100°C (layer top @l5
50 to ensure recovery of active ingredients such as MAM and MAA. The circulator, the liquid/force ratio (L/
G) = 1.0, and by adjusting the amount of nozzle gas supplied from the top of the tower with the fresh absorption liquid, the pH of the circulating liquid 70 at the bottom of the tower is set to 8. I managed OG.

The part of the circulating fluid that has absorbed MAM, etc., is the force extracted by the self-tube 100 at a temperature of 100°C (and the extractor or M
AM 7. OKg/Hr, MAA 13.9g/Hr
Hr.

M e OH2, OKg/llr, water 196.0
Kg/Ilr, caustic soda 13.0 Kg/Hr
It has a composition of
The layer was removed and was able to be recovered.

The water vapor exhaust gas that is absorbed and leaves the gas-liquid contact tower 30 has a mass of M A M 3.8 Kg/Hr, M A A
O,, IKg/llr, M e OH3B, 0,
It has a composition of Kg/llr, water vapor 3975.0 Kg/11r, and air 511.0 Kg/llr, and is introduced into the preliminary condensation tower 120 through a pipe 110. The pre-condensation tower is a shell with 25.4 mmφ*750 heat transfer tubes arranged in an equilateral triangle with a pitch of 50 mm.
It is a tube type.

49.4% of the total condensed components were condensed in precondensation column 120 and removed at 95° C. via drain 130 and discarded. The composition of the condensate is MAM 3.8Kg/llr
, MAA O,I Kg/Hr, MeOH3,8K
g/Hr, water 1975.0 g/llr, and the load of COD treatment was light.

The water vapor exhaust gas that has passed through the pre-condensation tower 120 without being condensed no longer contains MAM or MAA, and M e
OH34.2Kg/Hr, water vapor 2000.0K
g/llr, air 511.0 Kg/Hr, and a total condensation tower 15
0 is introduced. The total condensation tower is the same shell/tube type as the pre-condensation tower, and has a diameter of 25.4 mm*750.
The heat exchanger tubes are arranged in an equilateral triangle with pinch 501.

All the condensed components in the gas are condensed in the total condensation column 150, and M e OH34, OKg/Hr, water vapor 199
A condensate having a composition of 5.8 Kg/Hr is in the pipe 160.
It was taken out and recovered through. On the other hand, the non-condensable inert gas is mainly air-based, MeOHo, 2 g/
Ilr, water vapor 4.2.0Kg/Hr, air 5
It had a composition of 11.0 kg/llr and could be disposed of as a completely odorless gas through the exhaust pipe 170.

The recovered condensate was sent to a methanol distillation recovery column by a pump 180, and after distillation treatment until the methanol concentration reached 65%, it was circulated to the esterification step, making it possible to recover 85% of the methanol.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet diagram showing an apparatus for carrying out the present invention.

Claims (8)

[Claims] (1) In the process of producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify it, the waste liquid containing the sulfuric acid discharged from the esterification process is used. (hereinafter referred to as waste sulfuric acid solution) is neutralized with alkali.
When concentrating and recovering sulfate, unreacted methacrylamide and/or methacrylamide in the waste sulfuric acid solution is neutralized and concentrated by effectively generating water vapor from inside the waste sulfuric acid solution layer. A gas absorption operation in which the acid is separated from the waste sulfuric acid solution by entraining it with the generated water vapor, and the water vapor-based exhaust gas is brought into contact with water and/or an aqueous alkali solution under conditions where it can be treated as a substantially non-condensable gas. A method for recovering active ingredient 9 from exhaust gas, characterized in that the separated methacrylamide and/or methacrylic acid are absorbed and recovered in the water and/or alkaline aqueous solution. (2) The method according to claim 1, wherein neutralization and concentration are carried out by blowing steam and/or inert gas into the waste sulfuric acid solution. (3) The method according to claim 1, characterized in that the water and/or alkaline aqueous solution in which methacrylamide and/or methacrylic acid have been separated and absorbed is recycled to an esterification step and recovered as a methacrylic acid alkyl ester. . (4) The method according to claim 1, wherein the pH of the water and/or alkaline aqueous solution in which methacrylamide and/or methacrylic acid has been separated and absorbed is controlled to be maintained in the range of 7 to 10. (5) In a method for producing an alkyl methacrylate ester by reacting methacrylamide or methacrylic acid with a lower aliphatic alcohol in the presence of sulfuric acid to esterify it, the sulfuric acid-containing waste liquid discharged from the esterification step. (hereinafter referred to as waste sulfuric acid solution) is neutralized with alkali.
When concentrated and recovered as sulfate, unreacted methacrylamide and/or methacrylamide in the cough waste sulfuric acid solution is neutralized and concentrated by effectively generating water vapor from inside the waste sulfuric acid solution layer. When the acid and lower aliphatic alcohol are entrained in the generated water vapor and separated from the waste sulfuric acid solution, the water vapor exhaust gas is mixed with water and/or an aqueous alkaline solution under conditions that can be treated as a substantially non-condensable gas. The methacrylamide and/or methacrylic acid is absorbed into the water and/or alkaline aqueous solution and recovered by contacting and performing a gas absorption operation, and is recycled to the esterification process to be recovered as a methacrylic ester. From the steam-based exhaust gas that has been processed, 20 to 60% of the condensed components are first removed by partial condensation in the presence of an inert gas, and then the remaining uncondensed portion is completely condensed to obtain a low-grade A method for recovering active ingredients from exhaust gas, characterized in that a condensate containing an aliphatic alcohol is recycled and reused in an ertherization step. (6) The method according to claim 5, wherein an inert gas is introduced and mixed into the steam-based exhaust gas from which methacrylamide and the like have been removed, and then a partial condensation operation is performed. (7) The method according to claim 5, wherein neutralization and concentration are carried out by blowing steam and/or inert gas into the waste sulfuric acid solution. (8) The method according to claim 5, wherein the pH of the water and/or alkaline aqueous solution in which methacrylamide and/or methacrylic acid has been separated and absorbed is controlled to be maintained in the range of 7 to 10.